The present invention is directed to a process for forming polymeric seamless belts. More specifically, the present invention is directed to a process for forming biaxially oriented polymeric seamless or endless belts by a stretch blow molding process followed by heat setting and cooling of the resulting belt. One embodiment of the present invention is directed to a process which comprises providing a preform comprising a polymeric material, heating the preform to an appropriate stretching temperature at or above the glass transition temperature of the polymeric material and below the melting temperature of the polymeric material, placing the heated preform into a substantially cylindrical mold with a polished seamless inside surface, introducing a fluid under pressure into the heated preform while maintaining the preform axially centered in the mold, thereby causing the preform to expand both axially and radially without contacting the mold surface, subsequently causing the preform to expand until it contacts the mold surface, heating the expanded preform to an appropriate heat setting temperature above the stretching temperature and below the melting temperature of the polymeric material while maintaining fluid pressure, and subsequently cooling the set preform. Another embodiment of the present invention is directed to a process for preparing an electrophotographic imaging member which comprises preparing a seamless belt by the process of the present invention as detailed herein and coating onto the seamless belt a layer of a photogenerating material. Yet another embodiment of the present invention is directed to a process for preparing a dielectric receiver suitable as an imaging member for ionographic imaging processes.
Imaging members for electrophotographic imaging systems comprising selenium alloys vacuum deposited on rigid aluminum substrates are known. These imaging members require elaborate, highly sophisticated, and expensive equipment for fabrication. Imaging members have also been prepared by coating rigid substrates with photoconductive particles dispersed in an organic film forming binder. Coating of rigid drum substrates has been effected by various techniques such as spraying, dip coating, vacuum evaporation, and the like. Rigid drum imaging members, however, limit apparatus design flexibility, are less desirable for flash exposure, and are expensive. Flexible organic imaging members are manufactured by coating a web and thereafter shearing the web into segments which are then formed into belts by welding opposite ends of the sheared web. The resulting welded seam on the imaging member, however, disrupts the continuity of the outer surface of the imaging member and must be indexed so that it does not print out during an imaging cycle. Efficient stream feeding of paper and throughput are thus adversely affected because of the necessity to detect a seam within the length of each sheet of paper. The mechanical and optical devices required for indexing add to the complexity and the cost of copiers, duplicators, and printers, and reduce the flexibility of design. Welded belts are also less desirable for electrophotographic imaging systems because the seam forms a weak point in the belt and collects toner and paper debris during cleaning, particularly with wiper blade cleaning devices. Accordingly, seamless belts suitable as substrates for electrophotographic or ionographic imaging members are particularly desirable.
In addition, seamless belts for use in document handling systems in printing, copying, and duplicating apparatuses are particularly desirable. Document handler belts with seams tend to accumulate dirt in the seam area, thus necessitating frequent cleaning. When the document handler belts are in high volume copiers or duplicators generating over 100 copies per minute, it may be necessary to clean the document handler belt seams frequently. In addition, the seam of a document handler belt can provide a weak point with respect to belt breakage. Thus, a seamless document handler belt is desirable to reduce dirt build up on the belt and to reduce belt breakage.
Processes for forming biaxially oriented products by blow molding processes are known. For example, Soviet Union Inventor's Certificate 716,848 discloses a method for making drive belts from plasticbased materials by molding blanks from granules of polyethyleneterephthalate and blowing the blank in a mold so that the material is subject to biaxial orientation in mutually perpendicular directions, followed by thermally fixing the belt in a liquid-heat-carrier medium and cutting the tubular blank. According to this reference, the quality of the article is increased, on account of stabilizing the coefficient of orientation of the blank along its length, by carrying out the blowing while additionally limiting its size from below by using a bottom attachment to regulate the height. Additionally, Sovient Union Inventor's Certificate No. 305,074 discloses a method for the manufacture of drive belts which comprises molding a workpiece from polyethylene terephthalate resin granules, placing the workpiece in a mold, placing the mold containing the workpiece into a liquid heat carrier, introducing an inert gaseous heat carrier under pressure into the inner cavity of the workpiece heated to a state of softness to inflate the workpiece to the dimensions of the mold, and thermally fixing the inflated workpiece in the liquid heat carrier medium. The cylindrical portion of the inflated balloon is then cut into rings of required width.
In addition, U.S. Pat. No. 2,335,978 (Vogt), the disclosure of which is totally incorporated herein by reference, discloses a method of making containers such as flexible bags and liners for cartons. The method entails applying localized heat to the exterior surfaces of the wall portions of a container consisting of a flexible, thermoplastic sheet material which, when heated and rendered plastic, may be stretched lengthwise of the container and expanded circumferentially to increase its superficial area and which when again cooled will to a large degree retain its expanded condition. Application of heat softens the walls of the container, and a fluid pressure is subsequently applied within the container and a force is applied lengthwise to expand and lengthen the walls and increase their superficial area. Subsequently, the container is cooled in its expanded condition.
Further, U.S. Pat. No. 3,910,743 (Farrell), the disclosure of which is totally incorporated herein by reference, discloses an injection blow molding process wherein a semi-liquid and molten plastic is injected into a cavity into which a core rod extends. The molten plastic is discharged into the mold cavity and the material spreads in all directions around the core rod to fill the cavity and form a parison around the core rod. The core rod can be covered with an elastomer material which forms a balloon that hugs the core rod when the balloon is deflated. After a parison has been applied over the core rod, the core rod is withdrawn from the injection mold. Subsequently, the parison is blown by blowing into the parison or the balloon. According to the teachings of this patent, the plastic is injected into the cavity of the injection mold at the neck end of the core rod, and the application of the plastic to the surface of the core rod is then controlled by having a tube which surrounds the core rod and which fills most of the injection mold cavity. As the plastic material enters the mold cavity, the tube is withdrawn and the plastic material contacts the end face of the tube and advances as the tube withdraws so as to apply the plastic material to the core rod as a wave of plastic which rolls down the length of the core rod as the tube withdraws. U.S. Pat. No. 3,936,260 (Farrell), the disclosure of which is totally incorporated herein by reference, also discloses an injection blow molding process wherein the length to diameter ratio of plastic articles made on injection molding machines is increased without using long and relatively thin core rods. The first part of the blowing operation stretches the parison lengthwise before there is any substantial displacement of the parison in a radial direction. At the start of the blowing operation, a tube surrounds and confines radial expansion of the parison, but the tube is withdrawn progressively as the blowing operation continues. U.S. Pat. No. 4,363,619 (Farrell), the disclosure of which is totally incorporated herein by reference, discloses an apparatus and method for making a wide mouth container by an injection blow molding process wherein substantially the entire container is multiaxially oriented in its formation.
Additionally, European Patent Document 12, 481 (Neundorf et al.) discloses a hollow molding manufacturing process from partially crystalline polypropylene or ethylene-propylene copolymers. The process is carried out in one stage in the presence of benzoic acid, and entails cooling the parison to a temperature 10.degree. to 60.degree. C. below the melting range of the polymer and then reheating to the usual stretching temperature of 1.degree. to 20.degree. C. below the melting range and molding to a hollow body by biaxial stretching.
In addition, British Patent 2,089,276 (Reed et al.), U.S. Pat. No. 4,447,199 (Reed et al.), and U.S. Pat. No. 4,547,416 (Reed et al.), the disclosures of each of which are totally incorporated herein by reference, disclose a process for making biaxially oriented tubular articles which will provide bodies for processable food containers. The articles are made from an elongate tube of thermoplastic material as it emerges from an extruder. The process entails repeatedly performing a cycle which comprises engaging the tube by a first clamping means over a first region at a leading end of the tube and by a second clamping means over a second region at a spacing from the first region, so as to define between clamping regions a portion of the tube to be longitudinally stretched and radially expanded; moving the clamping means apart to stretch the tube portion longitudinally and admitting pressure fluid to the tube portion to expand it radially and form a bubble of biaxially oriented thermoplastic material adjacent to the leading end of the tube; and severing at least a substantial portion of the bubble from the tube to form the tube with a new end as the leading end of the tube for the succeeding cycle. U.S. Pat. No. 4,735,538 (Reed et al.) discloses a process of forming biaxially oriented tubular articles by repeating a cycle which comprises engaging a thermoplastic tube by a first clamping member over a first region at a trailing end of the tube and engaging the tube by a second clamping mechanism over a second region at a spacing from the first region so as to define between the clamping mechanisms a portion of the tube to be longitudinally stretched and radially expanded; admitting pressure fluid into the tube portion to expand it radially and form a biaxially oriented bubble adjacent to the leading end of the tube; and severing a substantial part, but not all, of the bubble from the tube to form the tube with a radially outwardly flared end as the leading end of the tube for the succeeding cycle.
Further, U.S. Pat. No. 4,499,045 (Obsomer), the disclosure of which is totally incorporated herein by reference, discloses a process for the production of tubes of a molecularly oriented plastic which comprises heating a plastic tube to a temperature at which stretching induces a molecular orientation and clamping a portion of the tube in a sleeve, followed by introducing a fluid under pressure into the portion of tube and moving the sleeve along the portion of the tube to cause its progressive radial expansion until it makes contact with a mold.
Additionally, U.S. Pat. No. 4,632,656 (Eyeglaar et al.) discloses an apparatus for manufacturing molecularly oriented plastic pipes. The apparatus includes a tubular mold of transverse dimensions equal to those of the pipe to be produced and equipped with a device for admitting a fluid under pressure into a region intended to receive the pipe section to be expanded. The apparatus also includes a member for closing and grasping one end of the pipe section of a tubular sleeve which opens into the mold by an end away from the closing and grasping member, the transverse dimensions of which correspond to those of the pipe section, and a means for causing a controlled relative axial displacement of the sleeve in relation to the closing and grasping member in which the open end of the sleeved is equipped with an annular plunger incorporating a surface of a frustoconical shape extending toward the inner wall of the mold and widened out in a direction away from the closing and grasping member. The apparatus produces pipe sections oriented in a reproducible manner and especially suitable for the construction of pipelines for fluids under pressure.
In addition, U.S. Pat. No. 3,733,309 (Wyeth et al.), the disclosure of which is totally incorporated herein by reference, discloses a hollow, biaxially oriented thermoplastic article, particularly a bottle, prepared from polyethylene terephthalate wherein the article has an inherent viscosity of at least 0.55, a density of about 1.331 to 1.402, and a ratio of article weight in grams to volume in cubic centimeters of about 0.2 to 0.005:1. If desired, the article thus formed can be heat set to achieve a uniform crystallinity in each article.
Also of interest are the following references: "Biaxially Oriented Polyethylene Terephthalate Bottles: Effects of Resin Molecular Weight on Parison Stretching Behavior," C. Bonnebat et al., SPE ANTEC Technical Papers, vol. 25, page 273 (1979); "Biaxially Oriented Poly(Ethylene Terephthalate) Bottles: Effects of Resin Molecular Weight on Parison Stretching Behavior," C. Bonnebat et al., Polym. Eng. Sci., vol. 21, no. 4, page 189 (1981); "Blowing of Oriented PET Bottles: Predictions of Free Blown Size and Shape," L. Erwin et al., Polym. Eng. Sci., vol. 23, page 826 (1983); "Stretch Blow Molding," S. L. Belcher, Modern Plastics Encyclopedia, vol. 64, page 206 (1987); "A Survey of Film Processing Illustrated With Poly(Ethylene Terephthalate)", Polym. Eng. Sci., vol. 18, no. 15, page 1163 (1978); D. V. Rosato and D. V. Rosato (Eds.), Blow Molding Handbook (1989); and "Meet `COFO`, a New Way to Make Multi-layer Parts," O. G. Raspor and J. Eichhorn, Plastics World, Feb. 1988, page 44. The disclosures of each of these references are totally incorporated herein by reference.
Although known molding processes are suitable for their intended purposes, a need remains for processes for preparing seamless belts suitable for electrophotographic and ionographic applications. In addition, a need continues to remain for processes for preparing seamless belts with excellent tensile strength. A need also exists for processes for preparing seamless belts with excellent thickness tolerances. Further, there is a need for processes for preparing seamless belts with multi-layer structures and excellent thickness tolerances for the layers. There is also a need for processes for preparing seamless belts with excellent surface uniformity. Additionally, a need exists for processes for preparing seamless belts that do not undergo any substantial degree of deformation upon being heated. Further, there is a need for processes for preparing seamless belts that are substantially transparent and exhibit little or no hazing as a result of the belt formation process. In addition, there is a need for stretch blow molding processes that enable preparation of seamless belts with a thickness of less than 0.010 inch, and frequently as low as 0.001 inch. A need also remains for processes for preparing seamless belts that are suitable as photoreceptor substrates and as document handler belts that exhibit reliability and require less frequent cleaning, thereby reducing costs. There is also a need for processes for preparing seamless belts with high surface quality in that the surfaces are smooth and free of defects.